The prior art has already proposed some solutions to fill this demand.
A first solution is illustrated schematically by FIG. 1 of the accompanying drawings. This Figure shows a circuit which comprises an operational amplifier of the single-ended type having an input terminal and an output terminal. The output terminal is connected to a plurality of outputs OUTi of the circuit through respective selection switches Swi.
A voltage signal Vin applied to the input terminal of the amplifier can be transferred alternately to a given output OUTi by driving its corresponding selection switch SWi. Each switch may be implemented with a CMOS transfer.
However, this prior solution only holds when the impedance of each load at the output end is comparatively high. In fact, the selection switches associated with each load should have a power-on resistance Ron which is much lower than the impedance of the corresponding load, in order to fully transfer the electric signal.
Assuming that a load of 30 Ohms is to be driven, the resistance Ron of the switch should then be less than 3 Ohms, and a MOS transistor of a huge size would be required to produce such a value. In addition, to design a circuit for operation on a power supply Vcc of just 3 Volts, p-channel MOS transistors with a W/L geometrical ratio of 50,000 to 1.2 and n-channel MOS transistors with a 10,000 to 1.2 ratio would have to be used. Due to such drawbacks, a second known solution, illustrated schematically in FIG. 2, has been employed hitherto.
This second solution basically provides for the switches to be shifted to somewhere ahead of the amplifier, specifically at the amplifier input end. This means, in essence, that an amplifier will be associated with each of the outputs OUTi.
While being an improvement on the previously described solution, this has a drawback in that an amplifier must be provided after each switch; accordingly, the solution is a costly one in terms of circuit layout and power consumption.
The technical problem underlying this invention is to provide a driver circuit, and method therefor, which have uniquely simple structural and functional features and such that electric loads, even low-impedance loads, can be driven alternately, thereby overcoming the limitations of the prior solutions.